Geochemical characterization of nasko gold deposits, north-western Nigeria

The geology, petrology and geochemistry of the rock types including quartzite, amphibole-schist and quartz-mica-schist from Nasko District, NW Nigeria were studied. The concentration of gold is found within the Maru schist belt located in the study area. These gold bearing quartz veins are associated with metamorphosed rocks which range in composition from semi pelitic-peliticmafic to ultramafic.

The rocks are peraluminous and highly enriched in the K cal-alkaline series based on several geochemical classification models. The quartz veins show low TiO₂/Yb and Nb/Yb ratio characteristic of back-arc basin basalt. The gold-bearing rocks are also highly siliceous with an average composition of SiO₂(81.91 wt %) and relatively average values of Al₂O₃, Fe₂O₃Na₂O and K₂O (9.15 wt %, 1.95 wt %, 1.64 wt % and 2.12 wt % respectively). The oxides of CaO, (1.09 wt %), MgO(0.80 wt %) and MnO(0.03 wt %) are low due to weathering in the study area.

Correlation of Au with the other trace elements analysed shows that Au is enriched and correlates positively with Co, Ba, Rb, Sr, Zr, V, Ni and also base metals which serve as indicator elements for Au. The range of values obtained by the fire-assay experiment indicates gold grades between 0.01–1.66 g/ton at a shallow depth of 1.2m. It is rather interesting to note that the gold grade increases with depth in the study area.